Especially in the field for piping of hazardous gases, it is customary to couple adjacent segments of tubing by means of a compression-type union. The tubing is generally made of metal, and each segment terminates at a hard peripheral sealing surface. The well-known VCR (vacuum compression rod) union is well-known and widely used in chip manufacturing installations, and exemplifies this field.
It is important that abutting sealing faces not be scarred, even minutely, by relative rotational movement during assembly. This is a uniform objective which is not always fulfilled. To avoid the unfavorable result, a purely compressive force should be exerted to make the seal.
There are other problems with conventional VCR fittings. There is a pervasive problem that, even with great care, residual twisting forces may be set into a completed piping structure. This frequently results in an untidy appearance of moderately out of line pipes, and worse, stored torsional forces which might ultimately lead to loosening of the unions. This can be a very serious consequence.
Attempts have been made to avert these consequences by placing in the union an anti-twist member. Such members are generally characterized as a compression cap with a tongue. One member of a threaded joinder abuts against the cap, and the tongue fits in an axial slot on the other threaded member. The slotted member is held against rotation, and the other member tightened down. This is a workable concept, shown in McGushion U.S. Pat. No. 5,054,822 filed Oct. 8, 1991.
Disadvantages of this earlier construction are the need to slot one of the threaded members with consequent extremely difficult deburring requirements, and that one of the threaded members, generally the male threaded member must carefully and very accurately be held against rotation or a counter-torque could be exerted in the system.
It is an object of this invention to provide a torque transfer fitting for a compression-type union which need not be. restrained at either of the threaded members, which can utilize unmodified male and female nut members which do not require deburring, which can utilize two identical parts, and which parts can be so short that they can be manufactured in an inexpensive press operation, rather than having to be machined.